A national register-based study of paediatric varicella hospitalizations in Denmark 2010-2016.

Varicella, usually a mild disease of childhood, can also cause complications and hospitalization. Universal varicella immunization is implemented in several countries worldwide, but not in Denmark. Taking advantage of unique national registers, we aimed to estimate the incidence of paediatric varicella hospitalizations and assess determinants for hospitalization. For this purpose, we designed a nationwide, retrospective register study of paediatric varicella hospitalizations and applied a case-cohort design and logistic regression analysis comparing hospitalized varicella patients to a sample of the entire paediatric population in Denmark. Varicella patients were identified in The Danish National Patient Register and referents were randomly selected from the Danish Civil Registration System. The incidence of paediatric varicella admissions was 11/100 000 children 0-18 years of age/year. Of admitted children 67·1% had complications and 30·0% had underlying disease. All categories of underlying disease significantly increased the odds of hospitalization as well as male gender and not having been born in Denmark. In conclusion, we found a considerable burden of paediatric varicella disease in Danish hospitals, of similar magnitude as in other European countries comparable to Denmark. With this study we have provided epidemiological data needed for considering implementation of varicella vaccine in Denmark.